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All trademarks are property of their respective owners 2014-08-0001

www.pericom.com

PT0516

8/27/14

12

PI5USB2549

USB Charging Port Controller and Load Detection Power Switch

Current-Limit Setting

The PI5USB2549 has an independent current limit setting that is programmed externally with a resistor. The ILIM setting is

The following equation programs the typical current limit:

Many applications require that the current limit meet specific tolerance limits. When designing to these tolerance limits, both

the tolerance of the PI5USB2549 current limit and the tolerance of the external programming resistor must be taken into

account. The following equations approximate the PI5USB2549 minimum / maximum current limits to within a few mA and

are appropriate for design purposes. These equations assume an ideal – no variation - external programming resistor. To take

resistor tolerance into account, first determine the minimum /maximum resistor values based on its tolerance specifications and

use these values in the equations. Because of the inverse relation between the current limit and the programming resistor, use

pin. Follow normal board layout practices to ensure that current flow from other parts of the board does not impact the ground

potential between the resistors and the PI5USB2549 GND pin.

Undervoltage Lockout (UVLO)

The undervoltage lockout (UVLO) circuit disables the power switch until the input voltage reaches the UVLO turn on threshold.

Built-in hysteresis prevents unwanted oscillations on the output due to input voltage drop from large current surges.

Thermal Sense

The PI5USB2549 protects itself with thermal sensing circuit that monitor the operating temperature of the power distribution

switch and disables operation if the temperature exceeds recommended operating conditions. The device operates in constant-

current mode during an over-current condition, which increases the voltage drop across power switch. The power dissipation in

the package is proportional to the voltage drop across the power switch, so the junction temperature rises during an over-current

condition. The thermal sensor turns off the power switch when the die temperature exceeds 135°C regardless of whether the

power switch is in current limit. Hysteresis is built into thermal sensor, and the switch turns on after the device has cooled by

approximately 20°C. The switch continues to cycle off and on until the fault is removed.

Application Information

Input and Output Capacitance

Input and output capacitance improves the performance of the device; the actual capacitance should be optimized for the particular

application. For all applications, a 0.1uF or greater ceramic bypass capacitor between IN and GND is recommended as close to the

device as possible for local noise decoupling. This precaution reduces ringing on the input due to power-supply transients.

Additional input capacitance 10uF or greater may be needed on the input to reduce voltage overshoot from exceeding the absolute-

maximum voltage of the device during heavy transient conditions or output shorting. Normally suggested the distance between IC

and DC supply is less than 15cm.

Output capacitance also needs to be close to IC as possible. When large transient currents are expected on the output, placing a

high-value low ESR electrolytic capacitor 100uF or greater on the output pin is recommended.